In one aspect, this invention relates to the separation of selected compounds in a pyrolysis gasoline stream mainly Isoprene with minimum energy consumption. Isoprene is separated from hydrocarbons by extractive distillation. In another aspect, this invention relates to the use of a mixture of sulfolane (tetramethylene sulfone) alone or in combination with water and thiophene oxides as the solvent (also referred to as extractant or entrainer) in the aforementioned extractive distillation.
Extractive distillation is a well-known technique for separating mixtures of components having a relative volatility close to unity (i.e., having nearly equal volatility and having nearly the same boiling point). It is difficult to separate the components of such mixtures by conventional fractional distillation. In extractive distillation, a solvent is introduced into a distillation column above the entry point of the feed mixture which is to be separated. The presence of the solvent in the column alters the relative volatility of the compounds present in a direction to make the separation greater, and thus, to require either fewer stages to effect the same separation or to make possible a greater degree of separation with the same number of stages. The solvent affects the volatility of the higher boiling feed component(s) sufficiently to facilitate the separation of the various feed components, and it exits with the bottoms fraction, as has been described.
The separation of isoprene, from a close-boiling C5 hydrocarbon mixture (pyrolysis gasoline) by extractive distillation is known and has been described. However, there is a need for the development of more selective solvents than those presently known in the extractive distillation of pyrolysis gasoline components to reduce the net energy consumption and capital investment and corrosion and water treatment related issues that are common with existing solvents. In particular, it is desirable to develop improved extractive distillation processes for producing isoprene of high purity, both with more selective solvents and by other techniques and combination of both, since this compound is an important starting material for various chemicals, polymers and rubbers.